This invention relates to a filter for filtering a flowing substance, such as oil, comprising a casing which is openable at one end, a substantially cylindrical, replaceable filter means fitted within the casing, the flow to be filtered being arranged to pass through the mantle of the filter means, and a collar for connecting the filter to the device assembly, which includes inlet and outlet ducts for the flow to be filtered.
One of the applications of encased cylindrical filters is filtering lubricating oil in combustion motors so as to keep the oil free of impurities in operation. A second typical field of application for filters of this type is filtering hydraulic liquid in hydraulic systems. Since the filter is fouled in operation and has to be replaced at intervals, the filter casing must be removable from the device assembly to which it is attached.
There are previously known oil filters, in which the filter means and the surrounding casing have been constructed as a solid unit, replaceable as such. However, such a design is a waste of material and also produces waste in abundance. From an ecological viewpoint, it is preferable to devise a casing that can be opened, so that the clogged filtering means alone is replaceable and the casing including a replacement means is put back in position in the device assembly. Patent application No. FI 955127 is cited as an example of such a design, in which the assembled oil filter described comprises a cylindrical, replaceable filter means, a perforated support pipe within the means, a collar as an extension of this pipe, a casing surrounding the means and a joint ring at the casing mouth. The collar has a thread, which connects the assembled filter with the device assembly, simultaneously providing a sealing between the joint ring and the device assembly.
In conventional filters of the type above, the casing must resist axial stress caused by the high pressure of the substance to be filtered, such as oil or hydraulic liquid, and for this reason the casing must be made of a rigid sheet material. The perforated support pipe must also be stiff enough to withstand the internal axial stress within the casing. However, the manufacture of such perforated pipes is awkward in terms of production techniques.
The purpose of this invention is to provide a filter with adequate resistance to the pressure within the filter casing caused by the substance to be filtered, and with the lower production costs than conventional filters. The filter in accordance with the invention is characterized by the fact that it includes a support member forming a solid extension of the collar, and consisting of an axial spindle inside the filter means and of an end flange at the end opposite to the collar, the periphery of the end flange being tightly sealed to the inner wall of the casing such that the support member will receive the internal pressure within the casing axially.
In a filter in accordance with the invention, the axial traction force caused by the pressure is not at all exerted on the casing, but merely on the spindle of the support member and on the end flange, thus allowing a thinner material thickness in the casing wall. If the filter is equipped with a perforated support pipe placed against the filter means, this may also be made thinner than before, which is a significant benefit in terms of manufacture techniques. Since the end flange sealed against the casing seals the pressurized casing interior to be filled with the substance to be filtered, the casing end does not have to be sealed as in conventional filters, but instead, the casing may be formed of a sleeve-like tubular piece which is open at either end.
In the filter in accordance with the invention, the support member including the spindle and the collar connecting the filter with the device assembly may be discrete components connected with each other by a threaded joint. In this manner, these components are joined by a joint with high mechanical strength and resistance to the traction force, which also is easy to open with a view to replace the collar, for instance. By a simple replacement of the collar, the filter is adaptable to threads of various sizes provided for the filter in the device assembly.
The filter in accordance with the invention preferably includes a joint ring between the openable casing end and the device assembly, the joint ring including one or more flow openings, through which the casing interior communicates with one or more inlet ducts for the flow to be filtered in the device assembly. In this case, the flow is steered into the casing outside the mantle of the cylindrical filter means, from where the flow is filtered inside the mantle, and eventually is removed via the inside of the collar into the outlet duct for filtered flow in the device assembly. In this case, the inner surface of the filter means may bear against the perforated support pipe, which can be advantageously manufactured of a thinner material than before, as indicated above.
The invention will be described in greater detail below by means of examples and with reference to the accompanying drawings, of which.